The usage conditions of a constant velocity universal joint are tending to be more severe in accompaniment with higher vehicle performance in recent years. The amount of heat generated by the constant velocity universal joint is trending upward due to the requirements of higher torque and high-rotation usage conditions. Also, the effect of radiant heat in a constant velocity universal joint for a drive shaft equipped on the differential gear side and a constant velocity universal joint for a propeller shaft is also trending upward due to layouts in which the distance from an exhaust pipe is reduced due space-saving measures. As a result, a boot mounted on the constant velocity universal joint is exposed to higher temperatures (e.g., 140° or higher).
Accordingly, in the particular case of a constant velocity universal joint that requires high heat resistance, there is a need to use a boot for a constant velocity universal joint made of silicone rubber, which is formed from a silicone rubber having excellent heat resistance (see Patent Document 1). The use of silicone rubber as a material is at the same time also excellent for low-temperature characteristics (e.g., −40° C. or lower). Also, cerium oxide, which is a compound containing a rare earth (a rare earth element), is sometimes included in the silicone rubber in order to further improve durability of the boot for a constant velocity universal joint at high temperatures.